Conventionally, cryopreservation has been performed for preventing cultured cells from cell deterioration with successive passages and contamination by germs so that the cells can be utilized for a long term. Known as such a general method for cell preservation is a method of preserving cells in liquid nitrogen (−196° C.) by: suspending the cells in a culture medium containing dimethyl sulfoxide (hereinafter, referred to as DMSO) and serum; dispensing the suspension in a cryotube or an ampule; and cooling the suspension with a program freezer.
Various compositions of preservation solutions for cryopreservation have been prepared depending on the types of cells to be preserved. For example, a serum-free culture medium for cryopreservation has been developed for cultured cells to be cultured in a serum-free culture medium (see, for example, Patent Document 1). In addition, a solution for cryopreservation varies in quality because of different serum lots. In addition, essentially unnecessary components for the preservation of cells, such as various kinds of cytokines, growth factors, and hormones contained in serum may change the property of the preserved cells, so solutions for cryopreservation using no serum have been developed (see, for example, Patent Document 2).
However, the serum-free cryopreservation solution disclosed in Patent Document 1 includes a basal medium containing a variety of components. For example, an RPMI1640 culture medium contains a large number of origin undefined amino acids. The influence of those culture medium components on the preserved cells is also unknown. In addition, purified albumin is used in Patent Document 2. However, it might be contaminated by various components depending on the degree of refinement of the albumin, so problems concerning influences on cells remain.
Considering the potential influences on cells to be preserved in solution containing serum or basal medium, especially for medical use, development of a chemically well-defined cell preservation solution free of natural animal-derived components is desired. Such a cell preservation solution includes origin-defined components, and thus, it can be expected to have an advantage that the quality of the solution is kept constant.
Unfortunately, conventional cell preservation solution needs basal medium, serum or serum replacement, such as serum albumins, purified albumins and the like to perform long-term and stable cell preservation. Therefore, a cell preservation solution that is totally free of natural animal-derived component has not been obtained yet    Patent Document 1: JP 63-216476 A    Patent Document 2: JP 2002-233356 A